How to Calculate Carbs in Cat Food (They're Not on the Label)
June 10, 2026 · Pawpoy Guides
If you’ve just been told your cat needs a low-carb diet, you’ve probably picked up a can of cat food, scanned the label for “carbohydrates”… and found nothing. That’s not a mistake. Pet food regulations don’t require carbs to be listed, so manufacturers almost never print them.
The good news: everything you need to calculate carbs yourself is on the label. It takes 30 seconds once you know the method.
What the guaranteed analysis tells you
Every pet food label includes a panel called the guaranteed analysis. It lists, at minimum:
- Crude protein (minimum %)
- Crude fat (minimum %)
- Crude fiber (maximum %)
- Moisture (maximum %)
Some labels also list ash, the mineral content left if the food were incinerated. Most don’t.
The carb math, step by step
Because every component of food must add up to 100%, carbohydrates are simply what’s left over after you subtract everything else:
Carbs (as fed) = 100 − protein − fat − fiber − moisture − ash
If ash isn’t listed, use an estimate: this calculator uses about 2.5% for wet food and 6.5% for dry food (commonly cited veterinary references use roughly 3% and 6%; the difference is small). Because ash is estimated, treat the result as an estimate, not an exact figure.
Example: a typical canned food
Say the label reads: protein 10%, fat 5%, fiber 1%, moisture 78%, ash not listed.
Carbs as fed = 100 − 10 − 5 − 1 − 78 − 2.5 = 3.5%
That sounds wonderfully low, but it’s misleading, because this food is 78% water. To compare foods fairly you need one more step.
Convert to dry matter basis
The dry matter basis (DMB) removes water from the picture:
Carbs (DMB) = carbs as fed ÷ (100 − moisture) × 100
Continuing the example: 3.5 ÷ (100 − 78) × 100 = 15.9% carbs on a dry matter basis.
That same “3.5% carbs” food is actually nearly 16% carbs once the water is excluded.
One honest caveat: this method uses the crude fiber figure on the label, which understates a food’s true fiber. As a result, the difference method tends to slightly overestimate carbohydrates, so the real number is usually a little lower than what the math gives. It is a good screening estimate, not a lab analysis.
Why this matters so much for diabetic cats
Cats are obligate carnivores; their natural diet is very low in carbohydrates. For cats with diabetes, many veterinarians favor lower-carb diets. The consensus guidelines (ISFM, AAHA) put the target at carbohydrates under about 12% of calories, roughly 3 grams per 100 kcal. That target is a percent of calories, not dry matter; the popular “under 10%” figure also refers to calories. Dry matter basis, which is what you can calculate from a label, is a close and convenient proxy: a food under about 10% carbs on a dry matter basis generally falls within that calorie-based target. Wet food is generally preferred over dry, and dry foods need starch to hold kibble together, which is why even premium kibble is often 25 to 40% carbs DMB.
The difference between foods can be dramatic, and it is invisible until you do this math.
Skip the math: use the free calculator
We built a free cat food carb calculator that does this exact calculation. Type in the guaranteed analysis from any label and you’ll get carbs on a dry matter basis instantly, including the ash estimate when it’s missing.
And if typing in numbers still feels like work: the Pawpoy app reads the label from a photo and runs this math for you, personalized to your cat. It’s free in early access and we’re onboarding gradually. Join the waitlist and we’ll email you when your spot opens.
Pawpoy is a decision-support and tracking tool, not veterinary advice. Always confirm food changes with your veterinarian, since every cat’s needs are different.